The Morita-Baylis-Hillman reaction for non-electron-deficient olefins enabled by photoredox catalysis.

Long-Hai Li,Min Shi,Yin Wei,Hao-Zhao Wei

doi:10.1039/d1sc06784b

Abstract

A strategy for overcoming the limitation of the Morita–Baylis–Hillman (MBH) reaction, which is only applicable to electron-deficient olefins, has been achieved via visible-light induced photoredox catalysis in this report. A series of non-electron-deficient olefins underwent the MBH reaction smoothly via a novel photoredox-quinuclidine dual catalysis. The in situ formed key β-quinuclidinium radical intermediates, derived from the addition of olefins with quinuclidinium radical cations, are used to enable the MBH reaction of non-electron-deficient olefins. On the basis of previous reports, a plausible mechanism is suggested. Mechanistic studies, such as radical probe experiments and density functional theory (DFT) calculations, were also conducted to support our proposed reaction pathways.

Highlights

The carbon–carbon bond-forming reaction is one of the most important transformations in organic chemistry, and has been and remains an important and fascinating area in organic synthesis
Key aminium radical intermediates that are generated via a single electron transfer (SET) process between the excited-state photocatalyst and amine substrates
Several recent reports suggested that a tertiary aminium radical derived from Select uor could undergo the addition to ole ns for the catalytic oxidative functionalization of alkenes.[45,46,47]

Summary

Introduction

The carbon–carbon bond-forming reaction is one of the most important transformations in organic chemistry, and has been and remains an important and fascinating area in organic synthesis. Edge Article remarkable emerging features in this body of recent literature is the frequency with which dual catalysis approaches are utilized.[10,11,12,13,14,15,16,17,18] Since rst being developed in 2015 by MacMillan's group,[19] quinuclidine and its derivatives as dual hydrogen atom transfer (HAT) catalysts in photoredox catalysis have enabled direct functionalization of substrates that are not readily oxidized by typical photocatalysts (Scheme 1B).[20,21,22,23,24,25,26,27,28] In a few cases, a quinuclidinium radical cation works as an oxidant that reacts with nucleophilic radicals or transient-metal intermediates through single electron transfer (SET).[29,30] as an electrophilic species, the quinuclidinium radical cation addition to ole ns has not yet been revealed.

Results

Conclusion